DENVER, Colo.— Recognizing the threat posed by expanding use of dangerous pesticides across 18 western states, competition from invading bullfrogs, nonnative diseases, and loss of wetlands, the U.S. Fish and Wildlife Service will announce tomorrow their conclusion that western populations of the northern leopard frog may warrant protection under the Endangered Species Act.

Scientists have been alarmed in recent years by severe declines in the populations of many native amphibian species, including the western leopard frog. In many cases, these declines are early indicators of problems such as pollution and disease that are degrading local ponds and wetlands.

“Western leopard frogs are the canary in the coal mine for our water quality across a large part of the country,” said Erin Robertson, senior staff biologist for the Center for Native Ecosystems. “When these frogs are at risk of extinction, we should be alarmed about the state of our wetlands and waterways.”

In 2006, a coalition of conservationists formally petitioned the Service to protect the western leopard frog and its habitat in the western United States under the Endangered Species Act. Tomorrow’s announcement is the long-delayed response to this petition.

“The western leopard frog was once abundant across 18 western states and parts of Canada,” said Jeremy Nichols, Climate and Energy Program director for WildEarth Guardians. “It has suffered serious declines across its range and is now locally extinct in some places. Without Endangered Species Act protection we stand to lose an invaluable part of our natural heritage.”

The western leopard frog has declined across its entire historic range, and trends continue downward (see map and table below). Scientists have been reporting declines since at least the early 1960s, and today the population is on the brink of extinction in several states — with declines ranging from 33 percent to nearly 100 percent — and showing no signs of slowing down.

“The northern leopard frog has proven invaluable for medical research with enzymes found in the frog’s body currently in clinical trials for use as a cancer treatment,” said Noah Greenwald, Biodiversity Program director for the Center for Biological Diversity. “Yet, today, the frog itself is severely endangered by a combination of habitat destruction, pollution, and invasive species.”

In Minnesota and other midwestern states, widespread reports of western leopard frogs with deformed limbs and bodies, including extra limbs, are believed to be tied to declining water quality. In 2002, the U.S. Environmental Protection Agency reported that more than 50 percent of streams, lakes, and ponds in California, Idaho, Missouri, New Mexico, Oregon, and South Dakota failed to meet state water quality standards. A study released by the U.S. Geological Survey also reported harmful levels of pesticide contamination in 87 percent of streams dominated by urban runoff and 57 percent of streams dominated by agricultural runoff.

“Atrazine, for example, was approved and applied by the megaton for 20 years to crops across the United States before even its most basic characteristics, such as its leaching properties, were known,” said Duane Short, Wild Species Program director for the Biodiversity Conservation Alliance. “After more than 20 years of drenching our soils with atrazine, scientific studies have recently linked the toxic substance to the spread of a deadly chytrid fungus among frogs. Land across the nation has become a killing field to frogs and other amphibians, and its time they get the protection they need.”

Pesticide use is increasing, threatening the western leopard frog. Atrazine, the most widely used pesticide in the United States, has caused reproductive deformities among populations throughout the west. Between the years 1991 and 2005, atrazine use increased by nearly 75 percent in the state of Minnesota.

The use of Roundup (a proprietary herbicide containing glyphosate), which is lethal to amphibians even at recommended levels according to recent studies, also threatens the western leopard frog. Roundup Ready crops (resistant to Roundup so the herbicide can be broadly applied to kill weeds) comprise a significant portion of crop acreage in the midwestern United States. In 2004, Roundup Ready soybean crops comprised 89 percent of all soybean crops in Iowa, 82 percent in Minnesota, 92 percent in Nebraska, 82 percent in North Dakota, and 95 percent in South Dakota.

The western leopard frog is closely tied to wetlands. Wetland declines of more than 50 percent are reported in the states of California, Colorado, Iowa, Missouri, and Nevada. In addition to pollution and habitat loss, the spread of invasive species like predatory bullfrogs and nonnative fish are also taking a serious toll.

The decline of the western leopard frog is another chapter in the global decline of amphibians. Of the 28 native frog species known from the entire United States, 19 have undergone major declines or suffered net population losses. In the western United States, 100 percent of the known frog species are declining. The major causes of frog declines include habitat loss and degradation, disease, water pollution, and climate change.